( 1140 ) 
In the rich collection of the Siboga Expedition T found about a 
hundred specimens of Siliceous Sponges, which I believe belong 
to the genus Spirastrella. | examined them as carefully as circum- 
stances allowed; moreover I studied about forty specimens from 
other localities, chiefly types of previous authors and for the greater 
part deposited in the British Museum. The result of this research is 
that I am convinced that we have to do with an uncommonly variable 
species; 32 of the 34 “species”, described by previous authors, 
and all the specimens of the Siboga collection belong to one single 
species, which, according to the rules of priority, has to be called 
Spirastrella purpurea (Lmk.) Rdl. 
If we look at the specimens macroscopically, we at once see differences 
so great, that any one would expect to have to distinguish a number 
of “species”. Sometimes they appear as thin encrustations on old pieces 
of coral, coralline algae ete, sometimes as thicker cakes with warty 
elevations. Another time they are club-shaped, or cylindrical with finger- 
shaped terminations, or cones, or pyramids. Others again have an 
irregularly spherical shape and form massive lumps. The colour is 
pale or bright yellowish, brown, grey ; sometimes bright carmine red. 
Among the enerustiag forms some are no more than 1 or 2 mm. thick; 
on the other hand we find massive specimens of 12 by 18 em. ; nay 
BowERBANK mentions one, which reached a height. of almost 2.5 me- 
ters. The surface is even, or provided with warty or digitiform eleva- 
tions; smooth or hispid. 
However, if we more carefully examine the specimens and then 
try to classify them into groups, we soon come to difficulties 
and we find e.g. specimens which might be placed in one group 
as well as in another. Thus we find that some crusts are on the 
whole very thin, but nevertheless show bere and there thicker regions; 
in fact we see the thin crusts gradually pass into thick cakes, or into 
specimens with warts, tubercles or finger-like processes. In some cases 
these processes have all about the same size; in other cases there 
is one main process with a number of smaller ones around it, 
gradually leading in this way to pyramidal cones with or without 
a few secondary processes at the base. Again in other cases the 
cylindrical processes are so long and numerous that they form the 
most characteristic feature of the sponge. Moreover, we may observe 
another phenomenon, viz. that neighbouring processes coalesce ; in fact 
we see e.g. clubshaped specimens pass into spherical, massive forms. 
From this state of things results the impossibility of making “spe- 
cies” on account of the external appearance; the extremes are united 
by all possible connecting links. 
